1. Field of the Invention
This invention pertains to a portable arc heater and more particularly it relates to a arc heated plasma lance.
2. Description of the Prior Art
A majority of coal-fired boilers employed by public utilities today use pulverized coal having heating values ranging from 7,000 to 14,000 BTU/lb, and often a high moisture content. In order to ignite the coal an external energy source is required which customarily has been satisfied by the use of spark-ignited oil or natural gas-fired lighters. Once boiler warning has been effected and the coal combustion has stabilized, the start-up lighters can be taken out of service as the coal combustion increases and the boiler reaches nominal power. Inasmuch as coal is graded according to volatility, moisture content and heating value, it is more or less difficult to ignite. In addition to this function, igniters may provide supplemental energy necessary to sustain and stabilize combustion under low stability conditions, such as cold or warm start-up, low load operation, and other transient operating conditions.
Auxiliary fuels, such as oil and gas, used for ignition have become increasingly expensive in the past decade. At the same time, auxiliary fuel consumption has increased because of the trend to cycling operation, the increased use of low rank or less stable coals, and the move toward lower turbulence/low NO.sub.x burners. For these reasons utilities are motivated to reduce their dependency on and consumption of auxiliary fuels. Accordingly, coal fired boilers operating on low grade coal are difficult and very expensive to start up with gas and oil. It is furthermore difficult to maintain combustion of the pulverized coal during turn-down cycles and therefore igniter systems are being utilized to minimize incomplete combustion or complete blackouts with the inherent risks of explosions.